There are a number of applications which would benefit from the use of conductive micro traces on a substrate, where the width of a micro trace as measured parallel to the surface of the substrate is 25 μm or less. In some of these applications, only the electrical properties of the conductive micro traces are significant, but others require consideration of the optical properties. Optical properties are significant if the micro traces are to be formed on vehicle or refrigeration windows to provide controlled window defogging and deicing or are to be formed on a plasma display panel (PDP) to control the level of electromagnetic radiation.
U.S. Pat. No. 5,071,206 to Hood et al., which is assigned to the assignee of the present invention, describes a filter arrangement which may be used for vehicle, housing and office windows. The Hood et al. patent states that the arrangement of layers for an optical filter should provide color correction, heat reflectivity and infrared reflectivity. The complexity in achieving a desired optical property is increased if the optical filter is combined with conductive micro traces for deicing or defogging.
Factors which must be considered within the design of an optical filter for a PDP include the degree of neutrality of transmitted color, the level of reflected light, the color shift with changes in the incidence angle of a viewer, and the transmission levels of infrared and electromagnetic radiation. FIG. 1 is one possible arrangement of layers to provide a filter for a PDP, which includes a module or separate glass sheet 10. An Etalon filter 12 is formed on a polyethylene terephthalate (PET) substrate 14 that has been affixed to the glass sheet by a layer of adhesive 16. Because a plasma display generates infrared radiation and electromagnetic radiation that must be controlled in accordance with legislated regulations, the filter layers 12 are designed to reduce undesired radiation from the display. Etalon filters based on multiple filter layers are used to screen infrared wavelengths and electro-magnetic waves. Interference between adjacent filter layers can be tuned to cause resonant transmission in the visible region, while providing desirable screening. FIG. 1 also includes an antireflection (AR) layer stack 18 that was originally formed on a second PET substrate 20. Antireflection layer stacks are well known in the art. A second adhesive layer 22 secures the PET substrate 20 to the other elements of FIG. 1.
The formation of conductive micro traces on a substrate for application to a PDP may be used to further reduce electromagnetic radiation. The tradeoff is that the presence of the micro traces may adversely affect the overall optical properties. A second concern is cost. A process for forming conductive micro traces is preferably able to achieve a small width dimension in a cost-efficient manner.